High Tech Electric Guitar. High School Senior Project

[WJS]

Questions
I've got to get a schematic for a good simple eq.
yes there are a million. and anyone who has ever used a tone stack calculator can tell you that there are an endless amound of posibilities.

for each channel I just need something simple maybe just a bass and treble with a high cut/pass
later on in the signal path I can add some better eqs.
any ideas or personal preferences?

This is for a guitar, but not for the standard magnetic pickups. I'm looking for something that will give a linear responce with the controls at zero (i e not a fender tone stack, not to bash or anything). I'd like to keep it simple, small and not to costly. preferably no inductors. and I'd like to cap. couple into and out of it and have it between the halfs of a tube.

any personal tastes?
just love the sound of a _____.?
I could just do a Baxandall but where would the fun be there.
is this the best option?

 

[WJS]

I posted some pics on my website. They are of the guitar I'm going to work on and some related stuff. More to come soon.

any comments?
(anyone ever put a new bridge on a guitar?)

 

[alk509]

[quote author="WJS"]I've never really worked with a preamp using bolth one hal of a tube for each polarity (1 tube per string). Its common to drive something push pull output tube wise but i'm not familiar with it in preamp form. how would this work? tubes biased class A? B? and then would there be distortion when one half switches off and the other on?[/quote]

I'm sure he meant one triode for each side of the balanced signal... the alternative is to use transformers (as you figured out), but they are not cheap... Also, power concepts don't really apply to preamps - read some preamp schematics to see how other people do it.

I'm with everyone else here... I get this uneasy feeling that you're in way over your head here, and STRONGLY suggest that you think about what you're doing before adding features and bells and whistles that make things more complicated for you, but not necessarily better (e.g., do you really need an EQ in there? Do the signals really need to be balanced? Do you really need the poly outs AND the pickup outs AND the mix out?).

Good luck!

Peace,
Al.

 

[mikka]

And don't forget to chase some skirt..........just to balance your dorky mind .... :green:

 

[pstamler]

[quote author="alk509"][quote author="WJS"]I've never really worked with a preamp using bolth one hal of a tube for each polarity (1 tube per string). Its common to drive something push pull output tube wise but i'm not familiar with it in preamp form. how would this work? tubes biased class A? B? and then would there be distortion when one half switches off and the other on?[/quote]

I'm sure he meant one triode for each side of the balanced signal... the alternative is to use transformers (as you figured out), but they are not cheap...[/quote]

Right -- one triode (half-12AU7) per input (half-pickup). Note that at some point, you may need to convert all those balanced signals to unbalanced by some means. Probably more tubes, or a transformer.

I'm with everyone else here... I get this uneasy feeling that you're in way over your head here, and STRONGLY suggest that you think about what you're doing before adding features and bells and whistles that make things more complicated for you, but not necessarily better (e.g., do you really need an EQ in there? Do the signals really need to be balanced? Do you really need the poly outs AND the pickup outs AND the mix out?).

Agreed. First things first; do the guitar mods, then figure out how many tubes the final project will use, given a relatively minimal circuit, then design and build your power supply. That power supply, for a minimum of eight 12AU7s, is going to be a non-trivial task.

Then build the 16 first stages. My guess is that will bring you up to graduation, which will leave you with summer vacation to track down ground loops and buzzes and things. While you're doing that, plan for the other stuff you want to build, like EQ and things, which probably should go into a second chassis, maybe with its own power supply.

Peace,
Paul

 

[WJS]

ok ok. sheesh
i dont think anyone thinks i can do this. anyway. i think i'm going to scale it back. just have a simple 12au7 per channel. no eq in the pre. no input tranies. power supply in a seperate box.
Elco and 1/4 in, 1/4 inch out.

anyone know a good place to pickup a rack mountable chassis?

 

[Scenaria]

I dont think its a matter of if you can do this rather its a question of a 3 week allotment.. thats tough

 

[StephenGiles]

Can,t see the point myself - guitar,lead, amplifier, good technique, that's all you need - listen to Jerry Donaghue.
Stephen

 

[mikka]

I believe you can do it. :thumb: If you combine self-belief with listening to old fogeys you'll go a long way....................and save yourself yonks of wasted heartache. Trust me.........I'm a politician.

 

[WJS]

to be honest i'm not that good at guitar. It isn't hard to understand why. I started playing so I could build the electronics.
I know the most important part isn't the electronics of the instrument being played but I wanted to be able to offer those who do have the good technique and everything an oppertunity to make their beloved guitars do more.
This isn't some sort of miracle guitar but just a way to squeeze a little bit more out of an already great instrument.

Thanks for the support I have a feeling i'm going to need it. and just to clarify the 3 weeks doesn't start for another 1.5 weeks.

anyway. I've been searching the net for a good way to take a balanced signal, run it into a tube and do it all w/o a tranie. Unless something hits me (hopefully an idea) I might just have to ground the shield in the pre, lift it on the guitar end, ground the - and run the + into the grid. Am I missing something?
I've never used " one half of the tube for each polarity"(-pstamler) before. This doesn't seem too complex but I cant seem to find an example. would anyone send me a schematic? or explain this a little more?
thanks in advance
-Bill

P.S. why didn't I find this site sooner?

 

[mikka]

One and a half weeks????????????????Got your guitar going yet?

 

[WJS]

sorry 1.5 weeks till the 3 weeks starts
4.5 or 5 weeks untill the deadline

 

[mikka]

I understood. Get to work.

 

[pstamler]

[quote author="WJS"]anyway. I've been searching the net for a good way to take a balanced signal, run it into a tube and do it all w/o a tranie. Unless something hits me (hopefully an idea) I might just have to ground the shield in the pre, lift it on the guitar end, ground the - and run the + into the grid. Am I missing something?
I've never used " one half of the tube for each polarity"(-pstamler) before. This doesn't seem too complex but I cant seem to find an example. would anyone send me a schematic? or explain this a little more?[/quote]

First, as you know, the 12AU7 has two triodes combined into a single glass envelope. One has its plate, grid and cathode on pins 1, 2 & 3 respectively, the other has them on pins 6, 7 & 8. So you take your two ends of the pickup and you run one end into pin 2 (which also has a resistor to ground) and the other into pin 7 (which ditto). Run the two plates from the primary of an output transformer designed for the purpose (more below).

Will this be a well-balanced circuit? Probably not, because the two triodes will likely have slightly different gains, and there are tolerances in the cathode resistors you'll be using as well. So common-mode rejection won't be all that great anyway.

Looking for a way to go from balanced to unbalanced without a transformer? Use a triode as an "anode follower"; put a 100k resistor from input to grid, and another from the not-hot side of the output coupling capacitor back to the grid. Put in a trimmer so you can get the gain set to approximately unity (the feedback resistor will need to be a little bigger than the input resistor). Put the non-inverted side of your balanced (amplified) signal into the input resistor of this tube. Now make another anode follower from another tube; put one 100k resistor from the output of the first anode follower to the grid; put another from the inverted side of your balanced (amplified) signal to the grid, and put a third from the non-hot side of *this* tube's output coupling capacitor to the grid. In effect, you're treating the first tube like an inverting op-amp, and the second one like a summing, inverting op-amp.

I didn't say it would be a good way. But it's a way. A better way is to make a differential op-amp from tubes, a la Fred Forssell. His designs work a lot better than what I outlined above.

Or you could find a transformer that will work with the typical high impedances of guitar pickups, and use it as an input transformer, running its secondary into the grid of a half-12AU7, which was your original idea. But if you find one -- which will be a struggle -- eight of them will cost a lot.

Frankly, though, I think you should try this first using the pickups unbalanced. Connect them balanced through the cable, like you proposed, but ground one end of each to the bottom of its tube's cathode resistor. Get fancy later.

Peace,
Paul

 

[WJS]

I was looking on
http://www.fairradio.com/audiot.htm
they have relitivly inexpensive stuff.
I dont want to buy any tranies yet because I dont know the impedence for the ghost pickups. they are per string and I believe, non magnetic.
Atleast for now i'm just going to ground the -.

Thanks for the explaination! very helpful. I think for the sake of not having too many tubes, I'm going to just ground the - or use a tranie. If the tranies cost less then the tubes and they will match the impedence correctly then i'll use em but it depends.

I like the Fred Forssell stuff very much, I might use his design depending on the requirements of the pre.
Thank you very much for the explaination and advice.

 

[Scodiddly]

Starting to sound like a more doable project... I don't think anybody is selling your skills short, it's just that we've all had to learn (the hard way) to break our projects into managable chunks. That way you can get something working and then expand (or build newer and better) in the next chunk.

 

[WJS]

I finaly spoke with graphtech, the people who make the polyphonic pickups. They are piezeo (sp?) and have an impedence around line level. I ordered a set and some tranies. they were really cheap and will give me a little bit of adjustability and let me keep the balanced signal.

Has anyone ever worked with this kind of pickup?
its my first time with something non magnetic.
I did get a few pointers:
short transmition lines <15 ft (I could only affort 10 anyway (@$2.50US))
and that the impedence is high, about line level.
I wonder what the tone is like, I've heard they sound kinda like an acustic but we'll see. do they have the same wierd middle responce that magnetics have (i doubt it but who knows)?

I guess I'll find out soon enough.

 

[Scodiddly]

You may need an input impedance up to about 8-10 Meg. No big deal, though - an FET will do that easily.

 

[WJS]

If its line, wouldn't I be able to run it almosy directly into a tube? I mean, tubes work with everything else thats line... would a FET really be needed?
I'm missing something

 

[pucho812]

Has anyone ever worked with this kind of pickup?

My buddy had a parker fly guitar that had them. I really liked how they sounded when combined with a normal humbucker pickup. Alone they were pretty good. again I like the idea of this guitar mianly to use in surround sound. imagine Vai playing his crazy stuff but in surround... :twisted: